The research will test the effectiveness of several complementary interventions designed to reduce intravenous drug-using patients' risks of contracting or transmitting AIDS. The project proposes to reduce AIDS transmission-related behaviors among patients using four types of clinic-based preventive interventions: (1) AIDS education (2) offering HTLV-III/LAV antibody testing (3) contingency contracting (4) peer support groups. The interventions are consistent with a social learning model of human behavior and are intended to: increase patients' motivation to change their high-risk drug use and sexual practices; inform them about safer practices and techniques; and provide both positive reinforcement and social support for desirable behavioral change. The research will be a quasi-experimental clinical study using multiple comparisons among methadone programs with random assignment to certain treatment conditions within each program. Three methadone programs will participate, two as "experimental" programs implementing the interventions and one as a "control". AIDS education will be offered to all patients in programs 1 and 2 (N=700). Subsequently, AIDS antibody testing will be offered to patients in program 1 who participated in education (N=280 est); testing will not be offered at program 2. Test results will be available to patients. finally, all known intravenous drug users in programs 1 and 2 (N=230 est) will be randomly assigned to one of three treatment intervention conditions: contingency contracting only (N=76), peer support group only (N=76), or contingency contracting with peer support (N=78). Program 3 will serve as a "pure" control, without any of the interventions. Assessments of change in patients' AIDS-related knowledge, attitudes, and high-risk behaviors (the outcomes) will be made at three times: baseline (prior to AIDS education), following the first intervention phase (after AIDS education and, in program 2, antibody testing), and following the second intervention phase (after contracting, peer support or both). Comparisons of outcomes will be made across the three programs at the three assessment times. Within-program comparisons of outcomes will also be made for the three treatment intervention conditions. Program 3 will provide a control for possible maturation and historical effects on outcomes.